1. Field of the Invention
This invention pertains to laser ceilometers and like instruments which include microprocessors that drive the instruments. More particularly, this invention pertains to an improvement to such laser ceilometers which is designed to increase their service life and reliability.
2. Description of the Prior Art
Laser ceilometers, such as those disclosed by the inventors herein in abandoned application Ser. No. 915,444, filed June 14, 1978 and pending application Ser. No. 24,779, filed Mar. 28, 1979, utilize laser diodes to direct radiation upwardly towards any clouds which may be present. This radiation then reflects off such clouds, and returns back to the laser ceilometer to be incident upon a photosensitive element, such as an avalanche photodiode. By measuring the time required for the radiation to be received at the photosensitive element, it is possible to ascertain cloud height.
In devices of this type, the laser diodes are usually pulsed rather than beam operated continuously. While the frequency with which the laser diode is pulsed may vary in accordance with a program executed by a microprocessor in the ceilometer itself, the laser diode is typically pulsed on the order of four times per minute for a period of perhaps 70 nanoseconds at a frequency of about 2.37 kHz. Typically, each pulse will have a power of approximately 20 watts.
Thus, it can be seen that the reliability of the instrument is limited by the reliability of the single laser diode used. It would therefore be advantageous to provide an improvement to a laser ceilometer which would have an increased service life not limited by the service life of a single laser diode.